A lubricating fluid such as a hydrocarbon oil is incorporated within and circulated through a refrigeration or gas compression circuit utilizing a helical screw rotary compressor to compress the working fluid. The lubricating oil performs multiple functions, one of which is to lubricate the moving parts of the compressor and to achieve sealing of the compression chamber defined by the moving parts, i.e. the intermeshed helical screw rotors within the casing bores during their rotation. Another is to cool the working fluid. The performance of the lubricant requires that the compression process and the lubricant itself be cooled. Conventionally, the oil miscible with the refrigerant working fluid or mixed with gas is discharged with the working fluid at a high pressure from the compressor, is separated from the working fluid in an oil separator and returned to the compressor. Typically, the oil is cooled within an oil cooler and is pressurized by an oil pump prior to injection into the compressor via injection ports opening to the compression process itself.
Compression systems utilizing helical screw rotary compressors employ conventional refrigerants such as R12, R22, R114, R500, and R502. However, with such refrigerants as R12 and R22, the lubricant tends to dissolve a very large quantity of refrigerant. Such refrigerants may start the compression process at a very low superheat level along with the high refrigerant entrained in a cooled oil. In some systems, air, helium, ammonia (NH.sub.3) may comprise the working fluid of the compression process, and attempts have been made to improve the isothermal efficiency of the compression process for these types of working fluids.
It is an object of the present invention to provide a compression system utilizing a helical screw rotary compressor where the working fluid may comprise highly superheated vapor at the inlet to the compression process.
It is a further object of the present invention to provide a compression system including a helical screw rotary compressor where the working fluid gas or vapor being compressed is not highly soluble in the compressor lubricant or compressor process cooling liquid utilized within the system and wherein the efficiency of compression is materially improved.